1. Field of the Invention
This invention relates to a sheet fastening apparatus and, more particularly, to a sheet fastening apparatus for fastening sheet bundles within an image forming apparatus such as a photocopier or within a sheet processor connected to the image forming apparatus.
2. Description of Related Art
Some sheet fastening apparatus for fastening partly a sheet bundle made of multiple sheets has been used in connecting to, e.g., an apparatus body of an image forming apparatus such as a photocopier. In such an image forming apparatus body, a sheet on which an image is recorded is conveyed from a prescribed outlet of the apparatus body at a prescribed time into a sheet fastening apparatus through an inlet of the fastening apparatus. The sheet is nipped by a pair of conveyance rollers in the sheet fastening apparatus and conveyed to a stock section at which sheets are temporarily stocked to pile sheets orderly until a prescribed number of sheets are stored. When a prescribed number of sheets are piled at the stock section, the image forming apparatus temporarily stops conveyance of sheets, and during this temporary stop the sheet fastening apparatus fastens sheets by staples or other means at designated positions on the sheet bundle made of multiple sheets.
Various sheet sizes and conveyance directions are used in image forming apparatuses these days, and number and positions of stapling may vary depending on users. To comply with those variations, a sheet fastening apparatus has been proposed capable of traveling a stapling mechanism or unit in a width direction perpendicular to the sheet conveyance direction and fastening sheets at multiple positions on a rear side in the sheet conveyance direction of the sheet bundles, which has been piled in the manner described above at the stock section. In this fastening apparatus, the sheet bundle fastened partially is nipped by a delivery roller disposed in the apparatus but having stayed away from the sheet bundle and another delivery roller opposed to the delivery roller and delivered onto a stock tray formed at a side of the apparatus. By repeating this operation, the fastening apparatus can pile sheet bundles each including a prescribed number of sheets on the stock tray, sequentially. The stock tray can move up and down in a direction that the sheets are piled up and travels downward in the piling direction corresponding to the thickness of the piled sheet bundles.
With such a conventional apparatus, however, the stapling unit has to move in the width direction perpendicular to the sheet conveyance direction to fasten one or more positions on the sheet bundle, so that such stapling operation takes much time and prevents the fastening apparatus from processing quickly. The stapling unit has to travel by about a sheet width, so that the stapling unit raises problems that the unit comes to have a complicated structure, consumes much electrical power for traveling, and becomes expensive.
With a conventional apparatus having a movable stapling unit, when fastening is performed in an oblique way to the sheet conveyance direction, the stapling unit is required to move further outward in addition to the normal traveling amount. However, it is difficult to place a number of guide rails to rotate the stapling unit obliquely corresponding to respective sizes of sheets, so that the fastening apparatus unit fastenes the sheets of only specific sizes.
Moreover, in the conventional apparatus which stacks sheets in a face down manner, the staples for fastening sheets are hit from a top face to a bottom face of the sheets, namely front side of the first page, and therefore, bent portions of a staple are projected from the bottom of the sheets. Furthermore, the sheet bundle is fastened by staples in a direction perpendicular to the sheet conveyance direction, so that the staples serve as conveyance resistance when the sheet bundles are conveyed bundle by bundle. It is difficult for such a conventional apparatus to convey the sheet bundles stably, and the apparatus cannot orderly pile up the sheet bundles.
It is an object of the invention to provide a sheet fastening apparatus capable of rendering a structure of the fastening apparatus simple, improving processing speed including stapling operation, and rendering conveyance of sheet bundles stable.
In one form of the invention to accomplish the foregoing objects, a sheet fastening apparatus includes sheet bundle conveying means for conveying sheet bundles, and sheet bundle fastening means for fastening sheet bundles, wherein the sheet bundle fastening means is disposed on either side, of the sheet bundles, extending substantially parallel with a sheet conveyance direction and fastens the sheet bundle at least at a position upon stop of conveyance of the sheet bundle by the sheet bundle conveying means.
According to the structure above, the sheet bundle fastening means is disposed on either side, of sheet bundles, extending substantially parallel in a sheet conveyance direction. For example, when the sheet bundle is fastened at two positions, a first stapling operation is done after the sheet bundle is conveyed to a prescribed position and stopped at the position, and then, a second stapling operation is done after the sheet bundle is conveyed to another position and stopped at the position. The sheet fastening apparatus can fasten the sheet bundles without traveling of the sheet bundle fastening means, thereby rendering the fastening apparatus structurally simple. The sheet fastening apparatus can shorten the time necessary for fastening sheet bundles, thereby greatly improving throughput of the fastening operation.
According to preferred embodiments, by disposing the sheet bundle fastening means so that fastenings extend parallel with the sheet conveyance direction on the sheet bundle, the conveyance resistance of the sheet bundle due to the fastenings is reduced to the minimum value. The sheet bundle fastening means may move pivotally as to direct the sheet bundle fastening means at any angle. This pivotable movement allows the sheet bundle fastening means to fasten any number of fastening means at any position and at any angle on either edge extending parallel to the sheet conveyance direction.
The sheet bundle conveying means can be placed on the same side as the sheet bundle fastening means to reduce positional shifts of the sheet bundles during conveyance of the sheet bundles. The sheet bundle conveying means may include a first sheet bundle conveying means and a second sheet bundle conveying means disposed on a downstream side of the first sheet bundle conveying means. In this embodiment, a conveyance speed V1 of the first sheet bundle conveying means is set equal to or less than a conveyance speed V2 of the second sheet bundle conveying means to convey the sheet bundles so that a tension is exerted to the sheet bundles, thereby conveying the sheet bundles having trued edges without disorder of the sheets.
In preferred embodiments, the sheet fastening apparatus has a third sheet conveying means placed on a downstream side in the sheet conveyance direction of the sheet bundle fastening means. After the sheet bundle arrives at the third sheet conveying means, the third sheet conveying means conveys the sheet bundle by nipping the sheet bundle, thereby reducing positional shifts of the sheet bundle during conveyance of the sheet bundles.
The sheet bundle fastening means may hit staples from a bottom face to a top face of the sheet bundles. By this structure, projections of bent staples come on the top face of the sheet bundles, thereby reducing conveyance resistance of the sheet bundles, rendering conveyance of the sheet bundles stable, and improving the piling property of the sheet bundles.
In one form of the sheet fastening apparatus, an arranging means for orderly arranging the edges of sheets in a width direction perpendicular to the sheet conveyance direction is provided traveling in the sheet conveyance direction in synchronism with the conveying operation of the sheet bundle conveying means during conveyance of the sheet bundles after arranging operation of the arranging means. The arranging means suppresses disorders of the sheet edges and brings stable conveyance of the sheet bundles. A roller pair may be disposed on a downstream side of the sheet bundle fastening means to make projections of staples flat, thereby making conveyance of the sheet bundles smooth. The roller pair may serve as a sensor for the staples.
In another aspect of the invention, a sheet bundle fastening means is provided on either side, left side or right side, of the sheet bundle, extending parallel with the sheet conveyance direction. When the sheet bundle is fastened at a single position in an oblique way, the sheet bundle fastening means having a home position at a position oblique with respect to the sheet conveyance direction fastens the sheet bundles at the oblique position after the sheet bundle""s edges are trued up. When the sheet bundle is fastened at two positions, the sheet bundle is moved to a prescribed position after the sheets are piled and sheets"" edges are trued up, and the sheet bundle fastening means moves pivotally in association with the sheet bundle""s movement. When the sheet bundle reaches the prescribed position, the sheet bundle fastening means already moves pivotally to a parallel fastening position and fastens the sheet bundle at two positions on the sheet bundle. Since this fastening apparatus can reduce time for stapling operation for the sheet bundles, the fastening apparatus can improve the throughput of the stapling operation.
To eliminate positional shifts of the orderly arranged edges of sheets when the sheet bundle is stapled at plural positions, the sheet fastening apparatus may perform orderly arranging operation of sheet edges at least one time in a direction crossing the sheet conveyance direction before respective fastening operations of the sheet fastening apparatus. This orderly arranging operation allows correcting the edges of sheet bundle even if shifted during conveyance of the sheet bundle, before respective fastening operations.